1. Fictional name of an Alien race ("Pod People"), from the 1955 novel "The Body Snatchers"

2. Seinfeld's Kramer

3. People detached from reality

Quote from Seinfeld episode s02e10 "The Appartment":

JERRY: Let me explain something to you.. You see, you're not normal. You're a great guy, I love you, but you're a pod. I, on the other hand, am a human being. I sometimes feel awkward, uncomfortable, even inhibited in certain situations with the other human beings. You wouldn't understand.